Last One - 4'x6' Steel, Epoxy and ClearPath servo's

[TeknicTom]

Yes, NIC 77, you have. I simply mentioned them because my responses in the beginning were largely directed to their comments. No offense intended.

The percentage of time that you can run at peak depends on many things. How long has the motor been running? How hot is the motor? What is the ambient? Are the cutting forces variable? What is the dynamic friction?

If the cumulative RMS torque has increased to 80% (for example) because the motor has been working near peak continuous capability for a period of time, there will be less margin to continue pushing the motor with peak torque. I realize this may be obvious but it it worth mentioning and partially explains why there is no magic number.

If you use too much peak torque for too long the motor will shutdown with a safety shutdown. Likewise, if you exceed the motor's continuous capability, it will also shutdown.

[1Jumper10]

Watch the video if you haven't. It's pretty informative. Peak current can be tolerated for 3 seconds. Nominal current can run 24/7. 100:1 inertia mismatch and even more is no problem. Aforementioned is from TeknicTom or the video he posted.

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[louieatienza]

No idea why you guys are talking about inertia matching. Not what I'm talking about at all. You need the inertia to calculate the torque required by the motor during acceleration. Inertia matching is to avoid overshoot or undershoot. Not looking to calculate an optimum gear ratio here, just to see what performance can be expected.

The formula you posted in another thread (and that I alluded to) from Kollmorgen's website states specifically that there is a gear ratio that will give the maximum acceleration, based on the torque and inertia of the motor. Servo systems are more tolerant of inertia mismatch because they are closed loop. Since steppers do not have feedback you have to be careful of inertia mismatch because you'll eventually start losing steps. A ballscrew is as much a reducer as a gearbox.

Not at all what I was looking for. The acceleration will take a fraction of a second, but then you may need to decelerate again after another fraction of a second. More, I was looking for a duty cycle, as in percentage of time that you can run at peak, or if there was a compromise between continuous and peak that can be used for these situations. What happens if you use peak too much, will the motor and controller automatically tone down the movements or do you just get a fault?

If your motors are continuously running in the IZ, then you've mis-sized them. Simple as that.

You make me sad Teknic Tom. So have I.

This is not a contest as to who gets more "brownie points". It's not often we have a representative from a manufacturer here, let alone one willing to share and assist with knowledge. I think if you dealt directly with Tom or one of the other applications engineers at Teknic about your specific machine and needs, they'd help you understand how they determine the size of the motors needed.

No. He's not. He's shooting for very fast top end speeds with very mediocre acceleration, and doesn't really know what he will get at the end of the day. I think he will be OK.

Mediocre acceleration to one is adequate or fast for another. If his idea of high performance is top end speed that's fine. You plan to use steppers, and expect servo-like acceleration performance.

[NIC 77]

The formula you posted in another thread (and that I alluded to) from ...................................

Again, I have no idea why you are ranting on. He has already bought the gear reducers. Not trying to find an optimal gear ratio here. Just curious how the system will perform.

If your motors are continuously running in the IZ, then you've mis-sized them. Simple as that.

Thanks Captain Obvious, but I was asking the expert from the company who makes them about his specific products.

You plan to use steppers, and expect servo-like acceleration performance.

Well, this thread is about 1Jumper10's build.

But since you brought it up.

I actually don't know what stepper acceleration performance can be. I've read that steppers can provide low to medium acceleration performance, while servos provide can provide high acceleration performance. I've seen some good servo system CNCs in various literature or youtube running between 0.5G and at the extreme end, 2G linear accelerations. Some of the really high end VMCs I've looked at had about 1G, the 2G was just one extreme example I saw.

So is the 0.2 to 0.25G really servo like performance? I don't really know, and unless someone can show me some quantitative figures (not just "high" or "medium" or "low" because those kinds of comments have no practical value), I won't know until I try it. I'll probably be happy with 0.15G at the end of the day, which I know is within stepper territory, but I am sizing my system to hit 0.25G if they can.

Also, you're mocking me and I don't appreciate it!

[NIC 77]

Yes, NIC 77, you have. I simply mentioned them because my responses in the beginning were largely directed to their comments. No offense intended.

The percentage of time that you can run at peak depends on many things. How long has the motor been running? How hot is the motor? What is the ambient? Are the cutting forces variable? What is the dynamic friction?

If the cumulative RMS torque has increased to 80% (for example) because the motor has been working near peak continuous capability for a period of time, there will be less margin to continue pushing the motor with peak torque. I realize this may be obvious but it it worth mentioning and partially explains why there is no magic number.

If you use too much peak torque for too long the motor will shutdown with a safety shutdown. Likewise, if you exceed the motor's continuous capability, it will also shutdown.

Thanks Tom,

I realize I can ask difficult questions or challenge ideas, but that is just the way I try to understand things. Thanks for your patience and answering my questions.

From what I've seen it does look like you have some very nice products, and of course your willingness to post in the forum is appreciated. Like I've said, I'd trade my steppers for your servos in a heartbeat. At the end of the day I don't think there is any question that your product outperforms steppers significantly.

[1Jumper10]

TeknicTom - thanks for taking the time to post. I know I'm more informed now than I was.

NIC77 - keep asking questions, it's hard to learn if you don't.

LouieA - thanks for sharing your experience. Your posts are always helpful and I've learned a lot from reading them.

Had a family emergency to deal with the last couple of days. But I was able to get one riser mostly fabricated. It is almost impossible to weld steel and keep it straight and square. The upright wasn't difficult to weld straight and square because it was just a tube on an angle iron. But we couldn't keep the gusset from pulling. It ended up pulling the corner of the angle iron up about 1/16". But we pretty much knew this was inevitable and the design is such that it makes no difference if it's out of square in the direction it pulled. It's not noticeable unless you set a straight edge against it and the gusset will be effective regardless of the symmetry.

I also ordered the leveling epoxy and that should be here next week.

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[louieatienza]

Hope all's well with your family...

[TeknicTom]

Same here...wishing you the best

[louieatienza]

Again, I have no idea why you are ranting on. He has already bought the gear reducers. Not trying to find an optimal gear ratio here. Just curious how the system will perform.

You have all the equations so you should be able to answer that yourself.

Thanks Captain Obvious, but I was asking the expert from the company who makes them about his specific products.

Didn't seem like it was obvious to you by the way you phrased the question.

Well, this thread is about 1Jumper10's build.

But since you brought it up.

I actually don't know what stepper acceleration performance can be. I've read that steppers can provide low to medium acceleration performance, while servos provide can provide high acceleration performance. I've seen some good servo system CNCs in various literature or youtube running between 0.5G and at the extreme end, 2G linear accelerations. Some of the really high end VMCs I've looked at had about 1G, the 2G was just one extreme example I saw.

So is the 0.2 to 0.25G really servo like performance? I don't really know, and unless someone can show me some quantitative figures (not just "high" or "medium" or "low" because those kinds of comments have no practical value), I won't know until I try it. I'll probably be happy with 0.15G at the end of the day, which I know is within stepper territory, but I am sizing my system to hit 0.25G if they can.

Also, you're mocking me and I don't appreciate it!

Those VMCs are using servos that range between 1-2kW. The steppers you have max out at something like 160W, with the added detriment of no positional feedback. So to expect 1/5 or 1/4 the performance of those VMCs when your steppers have about 1/7 the power of the smallest servos on the VMCs doesn't add up.

First off, you're not building anything that remotely resembles a VMC, you're building a gantry router. I will say, from experience as well as my calculations, that it would be very difficult to achieve .2--.25G with steppers, and still have accurate movement, with steppers, while still looking for the rapids you desire. I've already suggested that you won't get the performance you expect, with the components you have already selected.

Secondly, I'm just paying it back.

[NIC 77]

Louie,

Let’s not spoil the fun for everyone including ourselves regardless of who is or who isn’t to blame. Let’s just agree that we can’t get along and leave each other alone. I’d really appreciate it. I apologize for any offense I may have given you.

There is no need for you to respond to my posts in the future and I will show you the same courtesy.

[NIC 77]

1Jumper10,

I hope everything is well for your family.

I really do like seeing your workmanship. You're a very industrious and creative person.

[1Jumper10]

Thank you all for the kind thoughts. My father in law passed away suddenly on Tuesday. Funeral was today. Definitely a time for grief but I have a new appreciation for the love and kindness of my family and neighbors. My friend, who I built my second router for, is a surgeon and he cared for my father in law for about 15 years. Prolonged his life for easily, an additional 5 to 7 years. And in those extra years we got to share many milestones and see his grandsons (my son's) achieve many great things. When I am done with this machine or perhaps before, I want make him a nice placque or tribute of some sort for all he did for my father in law.

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[louieatienza]

My thoughts and prayers for your family...Hope you find comfort in creating... more than once I used what abilities I have to find escape, and dedicate my work, to the ones that passed me...

[1Jumper10]

Back at it.
Prepping for epoxy. I roughed up the primer coat with 60grit sand paper then wiped it all down with acetone. The forms are 1/8" high density board. Same stuff as peg board but no holes. I lined the parts that will be in contact with the epoxy with duct tape. No weather strip this time so I plan on sealing with either hot glue or some low viscosity epoxy.

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[1Jumper10]

Forms done. Need to seal it yet but that's enough for today. The epoxy pour will stop about 6" short of the ends. I'll bolt the I beams to the base there.

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[ger21]

Had to take a detour on my way to Mount Pleasant to avoid traffic, and drove through Freeland an hour or so ago, lol.

[1Jumper10]

Ha. You should have stopped in 😁

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[NIC 77]

I'm very sorry to hear about your loss. It sounds like he lived a full life and was surrounded by loved ones at the end. My condolences.

I'm looking forward to seeing how you pour this epoxy.

Do you have a target in mind for what acceleration you want on this build? What acceleration settings are you using on your friends router? I'll make some more graphs when I get a chance, been super busy for the past few days, and won't have time in the next two days to look at it. I'm going to change around my spreadsheet for rack and pinion to put it in the same format as the one I made for ballscrews where you can set the acceleration, and it tells you the cutting force available at different speeds.

The motors you mentioned before, SDSK3421P, putting that data in the spreadsheet I have already made for rack and pinion, with the new planetary gear inertia, and using a gear efficiency of 0.94 and a R&P efficiency of 0.9, you're looking at about 0.3G maximum with a rapid of 1000 to 1100 IPM. 0.3G also puts the acceleration torque below the continuous torque starting at about 1850 RPM or 910 IPM. A 400w servo would do better. There may be some factors that make it worse, but unless the torque vs speed graph from the manufacturer is conservative you won't do better. But still, I don't know, that sounds pretty good to me.

Like I said, I can post some better graphs and a sample calculation so you can see the math and formulas used and check it for yourself, when I have a bit more time. It's possible that I've made a mistake. Like everything in life, you have to take other people's opinions with a grain of salt and check it for yourself if in doubt.

There are other factors at play here obviously when you start looking at high accelerations, such as how well the rack and pinion handles acceleration, the force of the spring that holds the pinion in place, how stiff the system is (it's steel beam so I assume it will be pretty good ) etc, etc, that are obviously not included.

[1Jumper10]

Thanks for your condolences NIC -77.

Acceleration - lets see what it takes to get to .7G. I remember talking on the phone to Teknic tech support modelling the motors for the other router and when running their simulations it was said that they were approaching 1G. That router can move scary fast so I think .7G is a good starting point. .5G is probably a little more realistic.

Top speed- I would like to hit 1000 ipm but would be happy at 750 ipm.

Try modelling the https://www.teknic.com/model-info/CPM-SDSK-3421S-RLN/ If that doesnt hit the top speed goal try https://www.teknic.com/model-info/CPM-SDSK-3432P-RLN/

And remember that there are 2 motors driving the gantry.

The limiting factor in the drive system is probably max accell torque of the gearbox: 664 lb/in. And nominal output torque is 354 lb/in.

And it's looking like the gantry is going to weigh pretty close to 250lbs. See what numbers those return.

The epoxy will probably get here before next weekend. But it might be longer due to the 4th of July holiday.

[NIC 77]

Thanks for your condolences NIC -77.

Acceleration - lets see what it takes to get to .7G. I remember talking on the phone to Teknic tech support modelling the motors for the other router and when running their simulations it was said that they were approaching 1G. That router can move scary fast so I think .7G is a good starting point. .5G is probably a little more realistic.

Top speed- I would like to hit 1000 ipm but would be happy at 750 ipm.

Try modelling the https://www.teknic.com/model-info/CPM-SDSK-3421S-RLN/ If that doesnt hit the top speed goal try https://www.teknic.com/model-info/CPM-SDSK-3432P-RLN/

And remember that there are 2 motors driving the gantry.

The limiting factor in the drive system is probably max accell torque of the gearbox: 664 lb/in. And nominal output torque is 354 lb/in.

And it's looking like the gantry is going to weigh pretty close to 250lbs. See what numbers those return.

The epoxy will probably get here before next weekend. But it might be longer due to the 4th of July holiday.

I will definitely have a look at those and make some graphs for you when I get more time (a few days, I'm just swamped with something else at the moment), and give you a sample calculation so you can see the math and equations used for yourself.

The gantry weight obviously has to include everything that moves with the gantry, including motors, reducers, z axis, etc., but it's not as important a factor as you might think as the Load inertia is reduced by 1/GR^2.

I don't see any problems with the torque specs you listed. That gives a nominal input of 4Nm.

How much adjustability is there in the spring loaded plates that secure your gear and pinion into the rack? Is using a different pinion size out of the question? If it's not, I can try some variations there too.

I was actually wondering, what the acceleration settings are in the software for the router you made for your friend? Mach 3 or whatever you're using to control it? I'm guessing they are set at far less than the max the motors can do? As it stands, ignoring cutting forces, and only looking at peak power, with the SDSK3421, you're over a G up to about 300 IPM. That's about 0.35G at continuous output.

I'll probably be too busy to make any more posts for a few days, perhaps think about anything else you might want to try. We'll get it figured out.